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5 : Community-Onset Oxacillin-Resistant Staphylococcus aureus Infection
The osteomyelitic lesions of Egyptian mummies, the wound infections of medieval soldiers, and contemporary outbreaks of neonatal sepsis all point to one fact: Staphylococcus aureus is as old as medicine and is an extremely successful pathogen, capable of causing invasive disease at all stages of life. The genotypic changes responsible for the S. aureus confer cross-resistance to virtually all beta-lactam antimicrobials, including oxacillin and the other antistaphylococcal beta-lactams that are now most often prescribed. The recent whole-genome sequencing of S. aureus strongly supports the concept that horizontal gene transfer is a common evolutionary mechanism in S. aureus, even though staphylococcal cassette chromosome mec (SCCmec) transfer itself may only rarely occur; hence, horizontal transfer of mecA or SCCmec is a plausible hypothesis to account for emergence of community-acquired oxacillin-resistant S. aureus (ORSA) isolates that are dissimilar to health care setting acquired isolates. The clinical implications are obvious: treatment failure with accompanying complications or death may result if an antistaphylococcal beta-lactam antibiotic is used for serious infections and the infecting strain proves to be resistant; infections caused by oxacillin-resistant strains may be more difficult to manage or more expensive to treat, in part because vancomycin is inherently less efficacious; and the increasing prevalence of ORSA will inevitably increase vancomycin use, adding further to the problem of antimicrobial-resistant gram-positive bacteria. Immediate and widespread action to reduce vancomycin use can halt the emergence of fully resistant strains, increasing prevalence of the strains in health care settings, and then their eventual emergence in community settings.